“The interesting thing here is that this is an individual who sits on the House Committee on Science and Technology but somehow missed science class,” Mr. Obama said at a fundraiser in New York City Wednesday night. “But it’s representative of a desire to go backwards instead of forwards. And fights that we thought were settled twenty, thirty years ago.”

Meanwhile, Republicans Mitt Romney and Paul Ryan found themselves dragged into a debate over hot-button social issues and answering for differences between their personal positions on abortion, just days before a national convention aimed at showing a unified Republican party. The discussion lingered while President Obama and Romney tangled from afar over issues like education and the deficit.

The GOP ticket dealt with a renewed focus on abortion in the wake of Akin’s comments, remarks that have caused an uproar and generated demands from Romney and party leaders for the congressman to quit the race.

The questions over abortion overshadowed events by Romney and Ryan in the battleground states of Iowa, North Carolina and Virginia - three states which Obama carried in 2008 - ahead of next week’s Republican convention in Tampa, Fla. Obama rallied supporters in Nevada, the state with the nation’s highest unemployment rate of 12 percent, before heading to New York for a basketball-themed fundraiser.

Since selecting Ryan as his running mate, Romney has faced questions about how his policy positions differ from those espoused by Ryan, the architect of a controversial budget blueprint that would dramatically alter Medicare. On abortion, Romney does not oppose abortion in cases of rape and incest or if it will save the mother’s life, while Ryan does oppose abortion in cases of rape and incest.

Ryan, in an interview with a Pennsylvania TV station, emphasized Romney’s role at the top of the ticket, saying he was proud of his record on the social issue.

“I stand by my pro-life record in Congress. It’s something I’m proud of. But Mitt Romney is the top of the ticket and Mitt Romney will be president and he will set the policy of the Romney administration,” he said.

Ryan defended a bill he cosponsored in the House to permanently ban federal funding for abortion except in cases of incest and “forcible” rape. That language, which was eventually changed, would have narrowed the exception for rape victims. Akin and 225 other members of the House, including 11 Democrats, also cosponsored the bill.

Democrats have tried to tactfully steer the debate over abortion to appeal to female voters, including those living in hotly contested suburbs in battleground states such as Colorado, Florida, Ohio and Virginia. Mr. Obama did not address Akin’s comments while campaigning in Nevada, but his campaign honed in on the legislation related to federal funding for abortions.

Obama campaign spokeswoman Lis Smith said Ryan had “worked with Todd Akin to try to narrow the definition of rape and outlaw abortion even for rape victims.”

A new AP-GfK poll found that Obama maintained a slight lead among women voters, with 50 percent of women backing the president and 44 percent supporting Romney. The gender gap was similar to a finding in a June AP-GfK poll. Men were more closely divided in the latest AP-GfK poll, with 49 percent for Romney and 44 percent for Obama. In the suburbs, the candidates were closely divided, with 47 percent supporting Romney and 44 percent for Obama.

Akin, who is challenging Democratic Sen. Claire McCaskill in a race that could determine control of the Senate, was asked in an interview that aired Sunday if abortion should be legal in cases of rape.

Akin said: “If it’s a legitimate rape, the female body has ways to try to shut that whole thing down.”

Akin has refused to heed calls to step down and now would need a court order by Sept. 25 to leave the race. After that point, there would be no way to remove his name from the ballot. Ryan called the Missouri congressman and unsuccessfully urged him to exit the race, but he said he had no other plans to speak to him about it.

“He’s going to run his campaign and we’re going to run ours,” Ryan said of Akin.